Bony defect treatments for fractures, genetic malformations, tumors, and spine surgery often require implantation of grafts. Typical resorbable tissue engineering scaffolds should have sufficient porosity for bone cell as well as blood vessel ingrowth in orthopedic applications. Important factors in determining successful regeneration of tissue and organs include surface chemistry, porosity, micro- and macrostructure of the pores, and shape of the scaffolds.
U.S. Publication No. 20030055512 provides an injectable and moldable putty comprising biodegradable calcium-based compounds including calcium sulfate, hydroxyapatite, and tricalcium phosphate. Nevertheless, the patent application does not provide a bioabsorbable scaffold.
WO 2005/105170 relates to bone substitute compositions and methods of use. In a preferred embodiment, the composition comprises calcium sulfate-anhydrous, calcium sulfate-dihydrate and polyethylene glycol (PEG). CN 1724081 A provides a composite porous calcium sulfate scaffold with polymer, wherein the composite is prepared by dissolving polylactic acid or lactic acid/alcoholic acid copolymer or polyalcohol acid or polycaprolactone or polyhydroxy butyrate or polyhydroxy butyrate copolymer or polyanhydride in chloroform, stirring, proportionally mixing it with calcium sulfate, pouring in mould and drying. US 2002018797 (A1) relates to a nano-calcium phosphate/collagen composite that mimics the natural bone, both in composition and microstructure, as well as porous bone substitutes and tissue engineering scaffolds made by a complex of said composite and poly(lactic acid) (PLA) or poly(lactic acid-co-glycolic acid) (PLGA). US 2008281431 provides ceramic materials operable to repair a defect in bone of a human or animal subject, comprising a porous ceramic scaffold having a bioresorbable coating, and a carrier comprising denatured demineralized bone. This ceramic may contain a material selected from the group consisting of hydroxyapatite, tricalcium phosphate, calcium phosphates, calcium carbonates, calcium sulfates, and combinations thereof. However, the scaffolds in the above prior art do not provide sufficient compression stress resistance.
To maximize bone forming ability, the porous scaffold with 3-dimensional (3-D) structure is desirable to serve as an osteoconductive matrix. Due to its sponge-like structure, the porous scaffold usually cannot bear much physical load in the early stage of bone defect treatment. The porous scaffold tends to deform and loss pore structure under the load-bearing situation, thus it may not be good for some clinical applications which are under compression but still need to maintain space. For example, interbody fusion cage, a prosthesis used in spinal fusion procedures, should have adequate mechanical stability to support and transfer loads for maintaining foraminal height.
Thus there is a need to develop a bioabsorbable composite having advantageous mechanical properties in the early stage of implantation. After inserting the composite into the bone defect, the in situ formation of porous structures for composite scaffold by in vivo degradation.